Single fuel system carburetor having improved metering stability

ABSTRACT

The nozzle supplying fuel to the metering chamber of a single fuel system carburetor has a guide member that extends toward the entrance to the fuel-air passage connecting the metering chamber with the carburetor induction passage downstream of the carburetor venturi. Both the nozzle and the guide member, which can be integral with the nozzle, preferably lie on the axis of the fuel-air passage. The intake manifold pressure signal and the pressure signal of the carburetor venturi are blended to establish a metering pressure in the metering chamber. The difference between that metering pressure and a reference pressure existing above the liquid fuel level in the float bowl serves as a metering signal for the liquid fuel.

United States Patent Hideg [541 SINGLE FUEL SYSTEM CARBURETOR HAVING IMPROVED METERING STABILITY [72] Inventor: Laszlo Hldeg, Dearborn Heights, Mich.

[73] Assignee: Ford Motor Company, Dearborn, Mich.

[22] Filed: Aug. 14, 1970 [21] Appl. No.: 63,843.

[ 51 July 25, 1972 FOREIGN PATENTS OR APPLICATIONS Primary Examiner-Tim R. Miles Attorney-John R. Faulkner and Glenn S. Arendsen [57] ABSTRACT The nozzle supplying fuel to the metering chamber of a single fuel system carburetor has a guide member that extends toward the entrance to the fuel-air passage connecting the metering chamber with the carburetor induction passage downstream of the carburetor venturi. Both the nozzle and the guide member, which can be integral with the nozzle, preferably lie on the axis of the fuel-air passage. The intake manifold pressure signal and the pressure signal of the carburetor venturi are blended to establish a metering pressure in the metering chamber. The difference between that metering pressure and a reference pressure existing above the liquid fuel level in the float bowl serves as a metering signal for the liquid fuel.

12 Claims, 7 Drawing Figures mam m SHEEI 1 0F 2 PIC-3.3

FIG.2

\NVENTOR ATTORNEYS SINGLE FUEL SYSTEM CARBURETOR HAVING IMPROVED METERING STABILITY BACKGROUND OF THE INVENTION This invention is an improvement on the single fuel system carburetor described in U.S. Pat. No. 3,497,186 Hideg. That patent describes a carburetor in which a single fuel supply system replaces both the idling system and the main system found in virtually all present production carburetors. The single system eliminates difficulties in achieving proper metering during the transition phase when each of the previous systems is providing part of the fuel requirements and also improves fuel metering throughout the entire engine operating range.

Metering liquid fuel tends to be a relatively unstable operation because of liquid fuel surface tension, the presence of air and vapor bubbles in the liquid fuel, and turbulence in undesired locations in the air or air-fuel mixture. While the carburetor described in the patent minimizes many of these causes, the improved metering arrangement of this invention stabilizes the metering operation to a much greater extent.

SUMMARY OF THE INVENTION The improved carburetor of this invention has a carburetor body containing an induction passage with a venturi section therein. A throttle blade is located in the induction passage. The carburetor body includes a metering chamber separated from the induction passage but communicating therewith via a fuel-air passage that opens into the induction passage downstream of the throttle blade. A metering signal is established in the metering chamber. Liquid fuel is supplied to the metering chamber via a fuel supply mechanism that includes a fuel discharge member having a flow guide member extending into the metering chamber toward the entrance to the fuel-air passage.

A passage connecting the metering chamber with the carburetor venturi is used to establish metering pressure in the metering chamber. The relatively low intake manifold pressures produce an air flow through the passage that is proportional to the difference between venturi pressure and intake manifold pressure. A restricting jet included in the passage modifies air flow to provide a proper metering signal for engine idling and low speed operation. A relatively constant reference pressure that preferably is the total pressure in the air horn of the carburetor induction passage is established in the space above the liquid fuel level in the fuel bowl, and the metering signal is the difference between that reference pressure and the pressure in the metering chamber.

Best overall stability is obtained when the axis of the flow guide member is coincident with the axis of the fuel-air passage. A tube typically can be used as the fuel discharge member and the flow guide can be formed integrally with the tube by removing an elongated sector from the downstream portion of the tube to leave a small trough. A V-shaped trough improves metering stability over the circular trough but generally is more difficult to manufacture. Other trough shapes also can be used. In an alternate arrangement, the discharge member is cut off squarely and a wire or rod attached to its downstream end serves as the guide member. The rod preferably is mounted concentrically in the discharge member.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a sectioned elevation of a carburetor of this invention showing the location of the fuel discharge member on the axis of the fuel-air passage that connects the metering chamber with the carburetor induction passage.

FIG. 2 is an enlarged view of the fuel metering chamber that shows the structure of the fuel discharge member and flow guide.

FIG. 3 is a top view and FIG. 4 is an end view of the discharge member and flow guide of FIG. 2.

FIG. 5 is a top view and FIG. 6 is an end view of an alternate discharge member and flow guide in which the flow guide is a V-shaped trough.

FIG. 7 shows an alternate fuel metering chamber in which the flow guide is made from a small wire or rod mounted concentrically in the fuel discharge member.

DETAILED DESCRIPTION Referring to FIG. 1, a carburetor body 10 contains an induction passage 12 made up of an air horn portion 14 and a venturi having a converging portion 16, a throat l8 and a diverging portion 20. Throat 18 is considerably longer than the conventional venturi throat and a throttle blade 22 is mounted rotatably in throat 18 on a shaft 24. A choke blade 26 is mounted rotatably in air horn 14 on a shaft 28 and a flange 30 mounts the carburetor body 10 on the intake manifold 32 of an internal combustion engine. The choke blade is positioned by conventional temperature sensing mechanisms (not shown).

A fuel bowl 34 is located in carburetor body 10 adjacent induction passage 12. Fuel bowl 34 contains a float that operates a conventional valve mechanism to control the fuel level in the bowl. A tube 35 extends from the top of bowl 34 into air horn 14 where the tube opens upstream.

Body 10 also contains a metering chamber 36 that is located between induction passage 12 and fuel bowl 34. Metering chamber 36 is separated from the induction passage by a portion of the venturi wall and communicates with the induction passage through a tube 38 that defines a fuel-air passage 39. Tube 38 extends into induction passage 12 at a downward angle and terminates slightly beyond the centerline of the induction passage below throttle blade 22 where a plate 40 closes the downstream end of the tube. Plate 40 preferably lies in a plane approximately parallel to the axis of induction passage 12. A hole 41 is drilled into the lower surface of the downstream end of tube 38 so the axis of the hole lies on the approximate centerline of the induction passage.

The bottom of fuel bowl 34 contains a metering jet 42 that connects the bowl with a fuel passage 44. A metering rod 43 has its tapered portion located movably in jet 42. Fuel passage 44 in turn connects with a fuel discharge member 46 that opens into metering chamber 36. Member 46 is located directly across metering chamber 36 from the entrance to tube 38 and has its axis coincident with the axis of the tube. A fuel guide 48 is integral with member 46 and extends through metering chamber 36 toward the entrance of tube 38.

A valve member 50 is located in a second opening in the floor of fuel bowl 34. Member 50 is spring loaded by a spring 52 to an upper, closed position. Positioned directly above valve member 50 is the plunger 54 of a small vacuum motor 56. Plunger 54 is connected to a piston 58 in the vacuum motor. Piston 58 is spring loaded toward a lower position by a spring 60 and the upper chamber of vacuum motor 56 is connected by a hose 62 to intake manifold 32.

Linkage connecting throttle blade 22 with metering rod 43 includes a lever 64 fastened to shaft 24 outside of the carburetor. A rod 66 connects lever 64 to one arm of a bell crank 67 that has its other arm connected to metering rod 43. The bell crank is pivotally mounted on carburetor body 10 by a shaft 68.

A mechanism for establishing the metering signal in metering chamber 36 includes a signal passage 70 that connects the metering chamber with a small manifold 72. A metering jet 74 connects manifold 72 with venturi throat 18 above the closed position of throttle blade 22. A smaller high speed air bleed jet 75 connects manifold 72 with the converging portion I6 of the induction passage where jet 75 receives the impact of air flowing through induction passage 12.

During engine operation, air flows through jet 74, manifold 72, passage 70, metering chamber 36 and fuel-air passage 38 to the engine intake manifold. The air flow is relatively high at low engine loads and declines as increasing engine load increases intake manifold pressure and reduces the venturi pressure at jet 74. A pressure signal exists in the metering chamber that is a function of intake manifold pressure and venturi pressure and, at low loads, the restriction of jet 74. The difference between that pressure signal and the pressure existing above the liquid fuel level in fuel bowl 34 (the latter is the reference pressure existing in air horn section 14 by virtue of tube 35) is the fuel metering signal.

At engine idling and low operating loads, manifold pressure is relatively low and venturi pressure is relatively high. Considerable air then flows through passage 70 and the restriction of jet 74 establishes a minimum metering signal for drawing the proper amount of fuel into the metering chamber. At higher loads the venturi pressure declines and the air flow through passage 70 also declines. The restriction of jet 74 diminishes smoothly with declining air flow. Metering rod 43 is withdrawn from jet 42 according to the throttle blade opening so its taper adjusts fuel flow into the metering chamber according to engine requirements.

When the engine demands an enriched fuel-air mixture for full power acceleration, the high manifold pressure applied to the piston of vacuum motor 56 permits spring 70 to move plunger 54 into contact with the valve member 50, thereby opening the valve member to admit additional fuel into fuel passage 44. At high engine speeds and loads, jet 75 trims the fuel metering signal slightly to prevent excessive richness.

Turning to a consideration of FIGS. 2, 3 and 4 also, fuel discharge member 26 is a substantially circular tube having an elongated sector removed from its downstream end to leave a small trough that serves as the flow guide. The shapes of the flow guide member and the fuel discharge member are quite important in achieving stable fuel flow over a wide range of flow rates.

In the illustrated construction, which operates satisfactorily, the upper semicircular secton of the tube is removed from its downstream end back to an open face 80. Face 80 is substantially planar and preferably is within about plus or minus of a vertical plane when the tube is installed in the carburetor and the carburetor is mounted on an engine. The lower sector remains attached to the rest of tube 46 and defines an open trough 82 extending downstream of face 80. Each downstream corner of trough 82 is cut off so the trough comes to a sharp point 84 located on the lowest interior element of the tube. Point 84 typically is within one radius of tube 38 from the entrance to the tube and can be located within the tube ifdesired. Discharge member 46 preferably is made of brass or some other material that is wetted by liquid fuel.

At high flow rates, the discharge member issues a solid cylinder of fuel both from face 80 and trough 82. At the low flow rates occurring during engine idling, a thin segment of fuel flows only through trough 82. The surface tension of the liquid fuel wets the entire inner surface of trough 82 to the liquid acquires a highly stable crescent shape as indicated in FIG. 4 by numeral 86. High air velocities exist at the entrance of tube 38 throughout all engine speeds and these velocities do an excellent job of atomizing the liquid fuel approaching the end of trough 82 throughout all flow rates.

FIGS. 5 and 6 illustrate another useful fuel discharge member and flow guide in which the flow guide is a V-shaped trough 82 instead of the circular trough of FIGS. l-4. The V- shape of the trough preferably extends up to the plane of the face 80 of the discharge member where the V-shape blends smoothly with the circular interior of the discharge member as illustrated in FIG. 5. Since the liquid fuel acquires a more compact crescent shape as indicated at 86' in FIG. 6, the V- shaped trough produces more stable fuel flow at low flow rates.

In FIG. 7, the fuel discharge member 46 is cut off perpendicular to its axis and a small rod 90 is located concentrically in discharge member 46' so the rod projects into metering chamber 36 toward the entrance to fuel-air passage 40. The tip of rod 90 can be tapered as at 92 toward a sharp point 94. Rod 90 typically has a diameter equal to about one-half of the inner diameter of tube 46. Liquid fuel issues from the annulus formed between tube 46 and rod 90 and flows along the rod until it atomizes.

Atomized fuel and air passes through the fuel-air passage and exits into induction passage 12 through hole 41. Since the fuel is already atomized and mixed partially with air, it readily mixes with its remaining air complement in diverging portion 20. The location of hole 41 on the centerline of the induction passage assists in uniform mixing and distribution.

The axis of the fuel discharge member and flow guide preferably lies substantially on the axis of the fuel-air passage as illustrated, but acceptable metering stability can be achieved with constructions in which these axes intersect at various acute angles. In these latter constructions, the tip of the flow guide (point 84 or 94) preferably lies on or very close to the axis of the fuel-air passage.

Power valve 50 can be eliminated by modifying the linkage connecting the throttle blade to the metering rod to increase metering rod withdrawal during high power demands or by increasing the taper at the tip of the metering rod. The position of metering rod 43 also can be controlled partially or completely by a vacuum motor that senses intake manifold pressure.

Thus this invention provides an improved single fuel system carburetor that produces highly stable fuel flow even at low flow rates. The carburetor blends the venturi pressure signal with the intake manifold pressure signal to generate a pressure in the metering chamber that is used as a metering signal, and stabilizes liquid fuel flow throughout all anticipated flow rates.

I claim: 1. In a carburetor having a carburetor body containing an induction passage with a venturi section and a throttle blade located therein, a fuel metering system comprising a metering chamber located in the carburetor body, said metering chamber being separated from the induction passage but communicating therewith via a fuel-air passage means, said fuel-air passage means opening into the induction passage downstream of the throttle blade,

means for establishing a metering signal in said metering chamber, and

fuel supply means for conducting fuel to the metering chamber in response to the metering signal established therein, said fuel supply means including a fuel discharge member extending from a fuel passage means into the metering chamber toward the entrance of said fuel-air passage means, and a flow guide located at the downstream end of the fuel discharge member, said flow guide being integral with the fuel discharge member, said integral flow guide and discharge member comprising a tube having one end connected to said fuel passage means with an elongated sector cut out of the other end to leave a trough extending toward the entrance to the fuel-air passage means.

2. The carburetor of claims 1 in which the means for establishing a metering signal comprises passage means connecting the metering chamber with the venturi section above the throttle blade, and a restricting jet located in said passage means.

3. The carburetor of claim 1 in which the fuel-air passage means is a tube extending into the induction passage and having an exit opening on the centerline of the induction passage.

4. The carburetor of claim 1 in which the axis of the fuel discharge member lies substantially on the axis of the fuel-air passage means.

5. The carburetor of Claim 2 in which said flow guide tapers to a point at its downstream end.

6. The carburetor of claim 3 in which the trough has a V- shaped cross section.

7. The carburetor of claim 5 in which the means for establishing a metering signal in the metering chamber comprises passage means connecting the metering chamber with the venturi section above the throttle blade and a restricting means located in said passage means.

8. The carburetor of claim 6 in which the means for establishing a metering signal in the metering chamber comprises a second restricting means opening into said passage means from the converging portion of said venturi section.

9. The carburetor of claim 7 in which the fuel-air passage means is a tube extending into the induction passage and having an exit opening on the centerline of the induction passage.

[0. A carburetor for an internal combustion engine comprising a carburetor body containing a fuel bowl, a fuel metering chamber and an induction passage having a venturi section, said venturi section having a converging portion, a throat, and a diverging portion,

a throttle blade located in said induction passage downstream of at least a portion of the throat of said venturi,

fuel-air passage means connecting said metering chamber with said induction passage downstream of said throttle blade,

fuel supply means connecting said fuel bowl with said fuel metering chamber for supplying liquid fuel to said metering chamber, said fuel supply means comprising a fuel discharge member extending into said metering chamber toward the entrance of said fuel-air passage means, said fuel discharge member having a flow guide member tapering to a point at its downstream end, said point being located within about one radius of the fuel-air passage means from the entrance to said fuel-air passage means,

a conduit connecting the upper portion of said fuel bowl with the induction passage upstream of the venturi section, and

passage means connecting the venturi throat with said metering chamber, said passage means conducting air from the venturi throat to said metering chamber and said fuelair passage means conducting air from said metering chamber to said induction passage downstream of the throttle blade, said passage means and said fuel-air passage means establishing a pressure in said metering chamber that is a function of the venturi throat pressure and the pressure in the induction passage below the throttle blade, the pressure in said metering chamber relative to the pressure in the upper portion of said fuel bowl being a metering signal that draws fuel into the metering chamber.

11. The carburetor of claim 10 comprising a restricting jet means at the opening of said passage means into the venturi throat, said. jet means establishing a pressure drop in said passage means at low engine speeds and loads to provide an increase in said metering signal.

12. The carburetor of claim 11 in which the fuel-air passage means extends into the induction passage and communicates with the induction passage through an opening located on the induction passage centerline, said opening facing in a downstream direction. 

1. In a carburetor having a carburetor body containing an induction passage with a venturi section and a throttle blade located therein, a fuel metering system comprising a metering chamber located in the carburetor body, said metering chamber being separated from the induction passage but communicating therewith via a fuel-air passage means, said fuel-air passage means opening into the induction passage downstream of the throttle blade, means for establishing a metering signal in said metering chamber, and fuel supply means for conducting fuel to the metering chamber in response to the metering signal established therein, said fuel supply means including a fuel discharge member extending from a fuel passage means into the metering chamber toward the entrance of said fuel-air passage means, and a flow guide located at the downstream end of the fuel discharge member, said flow guide being integral with the fuel discharge member, said integral flow guide and discharge member comprising a tube having one end connected to said fuel passage means with an elongated sector cut out of the other end to leave a trough extending toward the entrance to the fuel-air passage means.
 2. The carburetor of claims 1 in which the means for establishing a metering signal comprises passage means connecting the metering chamber with the venturi section above the throttle blade, and a restricting jet located in said passage means.
 3. The carburetor of claim 1 in which the fuel-air passage means is a tube extending into the induction passage and having an exit opening on the centerline of the induction passage.
 4. The carburetor of claim 1 in which the axis of the fuel discharge member lies substantially on the axis of the fuel-air passage means.
 5. The carburetor of Claim 2 in which said flow guide tapers to a point at its downstream end.
 6. The carburetor of claim 3 in which the trough has a V-shaped cross section.
 7. The carburetor of claim 5 in which the means for establishing a metering signal in the metering chamber comprises passage means connecting the metering chamber with the venturi section above the throttle blade and a restricting means located in said passage means.
 8. The carburetor of claim 6 in which the means for establishing a metering signal in the metering chamber comprises a second restricting means opening into said passage means from the converging portion of said venturi section.
 9. The carburetor of claim 7 in which the fuel-air passage means is a tube extending into the induction passage and having an exit opening on the centerline of the induction passage.
 10. A carburetor for an internal combustion engine comprising a carburetor body containing a fuel bowl, a fuel metering chamber and an induction passage having a venturi section, said venturi section having a converging portion, a throat, and a diverging portion, a throttle blade located in said induction passage downstream of at least a portion of the throat of said venturi, fuel-air passage means connecting said metering chamber with said induction passage downstream of said throttle blade, fuel supply means connecting said fuel bowl with said fuel metering chamber for supplying liquid fuel to said metering chamber, said fuel supply means comprising a fuel discharge member extending into said metering chamber toward the entrance of said fuel-air passage means, said fuel discharge member having a flow guide member tapering to a point at its downstream end, said point being located within about one radius of the fuel-air passage means from the entrance to said fuel-air passage means, a conduit connecting the upper portion of said fuel bowl with the induction passage upstream of the venturi section, and passage means connecting the venturi throat with said metering chamber, said passage means conducting air from the venturi throat to said metering chamber and said fuel-air passage means conducting air from said metering chamber to said induction passage downstream of the throttle blade, said passage means and said fuel-air passage means establishing a pressure in said metering chamber that is a function of the venturi throat pressure and the pressure in the induction passage below the throttle blade, the pressure in said metering chamber relative to the pressure in the upper portion of said fuel bowl being a metering signal that draws fuel into the metering chamber.
 11. The carburetor of claim 10 comprising a restricting jet means at the opening of said passage means into the venturi throat, said jet means establishing a pressure drop in said passage means at low engine speeds and loads to provide an increase in said metering signal.
 12. The carburetor of claim 11 in which the fuel-air passage means extends into the induction passage and communicates with the induction passage through an opening located on the induction passage centerline, said opening facing in a downstream direction. 